CAEBONIFEROUS BRACHIOPODA. 
299 
the valve, they become so small, and pass so obliquely through the substance of the 
shell as to be almost invisible. The two frontal spines and those on the auricular 
expansions pass right through the outer thickness of the shell, and open on the interior 
mth a raised rim or rounded margin (Sup., PI. XXXVI, fig. 16 s). The borders of both 
valves, as in Frod. semireticulatus, were ornamented by one or two rows of irregular 
tubular spines that passed through the shell. This latter character is well seen upon 
internal casts of the shell. - 
" 6 A. Prodiictus longispinus, var. spinosa, Sow. — An etched specimen of this variety 
shows but a single row of pores between the ribs on the upper portion of the shell, 
whereas on the same part of the shell of the typical variety of P. longispinus, which 
has the two well-marked frontal spines, there are three or more rows of pores, which are 
generally planted upon the ribs and not between, as in the other variety. 
" 7. Prodiictus sinuatus. — The perforations in this species are much after the same 
character, and quite as numerous, as those seen in P. lojigispiniis, and, as in it, the per- 
forations change their character below a certain line on the ventral valve, being smaller, 
more oblique, and much less distinct. The frontal portion of the dorsal valve is pierced 
by one or two irregular rows of tubular spines that pass through the shell and appear as 
tubercules on the inner surface of the valve. 
" 8. Produdus Youngianus, — I have not been able to detect any perforations in the 
shell of this species. The internal surface of the dorsal valve shows numerous small 
tubercules, which are probably the continuation inwards of external tubular spines. 
" 9. Produdus aculeatus. — I have looked at numerous specimens of this species, but 
have failed in finding any evidence of perforations on either inner or outer surface of the 
shell. 
"10. Produdus spinulosiis. — The numerous spines in this species appear on the inner 
surface of the valves as raised tubercules, and amongst these I have detected small, 
irregular, widely placed perforations passing outwards in the shell. These perforations 
do not appear to be more numerous than the spines. 
"11. Produdus mesolobus. — On slightly decortica.ted examples of this species its 
comparatively smooth shell is seen to be perforated by numerous, small, oblong punctures, 
which, I think, extend outw^ards to the surface of the shell, on at least the ventral valve. 
The inner surface of the dorsal valve is quite smooth in some specimens ; in others it is 
covered by small, oblong tubercules, and the few, widely scattered, tubular spines appear 
to pass through the thickness of the shell and impress themselves on the inner surface of 
the valves as raised tubercules. If I am right in thinking that we have the outer layer of 
shell preserved in this species, then it is the only Produdus I know that shows perfora- 
tions on the outer surface of the shell ; and it presents the further peculiarity of showing 
■ no perforations on the inner surface of the dorsal valve. After looking long and carefully 
at the species I think I am nearly correct in what I have stated. 
" 12. Produdus cora.—On\y on two examples of this species from different localities 
39 
